During combustion in internal combustion engines, exhaust gases are produced which contain, among other things, nitrogen oxides, NOx, which are harmful to humans. These gases are channeled away from the engine by way of an exhaust system. In addition to the fumes that are produced during combustion of fuel in an internal combustion engine, a relatively large amount of noise is also generated and the sound waves pass through the exhaust system with the exhaust gases. The noise generation requires muffling in order to meet current regulations relating to noise pollution.
Previously proposed muffling systems use baffles and expansion chambers positioned along the exhaust pipe to dampen the sound. A problem with such an arrangement is that temperature gradients are created which leads to backpressures being created in the exhaust manifold, which, in turn leads to an increase in temperature in the exhaust manifold. The backpressure acts as a resisting force against the pistons and crankshaft, which reduces the efficiency of the engine. The backpressure varies according to the amount of exhaust gas being produced, which is a function of the number of revolutions of the engine.
When a vehicle is started, it takes some time for a catalytic converter on that vehicle to heat up to a temperature at which it operates efficiently. Current catalytic converters take some time to heat up to the required temperature when the vehicle is started.
There is an underlying desire to produce an exhaust filter that reduces harmful emissions and improves fuel economy, whilst also reducing the noise pollution and reduces the back-pressure, which in turn improves engine torque, power and efficiency.